In the case of the known method, the known communication station and the known data carrier the communication station first generates an interrogation signal during an interrogation cycle and transfers this to all the data carriers present in the communication range of the communication station. The communication station is then set to transmitting and the data carrier to receiving. Subsequently, the communication station is switched from transmitting to receiving and the data carriers are switched from receiving to transmitting, after which the data carriers responding to the previously received interrogation signal transmit their response signals to the communication station. The transmission of the response signals from the data carriers to the communication station is then effected in so-called time slots, a given number of time slots being selected and each data carrier being assigned to a time slot on the basis of the serial number of each data carrier.
Within such a time slot one or more data carriers first of all each transfer a response signal to the communication station. In this time slot the communication is subsequently switched from receiving to transmitting and at the same time the data carrier or data carriers are switched from transmitting to receiving. This first switching operation within a time slot requires a certain switching time. Subsequently, the communication station transmits the acknowledge signal, which is a positive acknowledge signal when only one data carrier has transmitted a response signal to the communication station in the relevant time slot, or which is a negative acknowledge signal when more than one data carrier has transmitted a response signal to the communication station in the relevant time slot. After the transmission of the acknowledge signal another switching operation is effected, i.e. the communication station is now switched from transmitting to receiving and the data carrier or the data carriers are switched from receiving to transmitting. This switching operation also requires a certain switching time within a time slot. Thus, in the known method two switching time intervals occur in each time slot, which has the disadvantage that the length of an interrogation cycle is comparatively great and, consequently, the time required for unambiguously identifying all the data carriers present within the communication range of the communication station by means of a plurality of interrogation cycles is comparatively long.
Moreover, the known solutions exhibit the problem that the acknowledge signals, which are digital signals representing one bit or a bit string having a plurality of bits, are transmitted from the communication station to the data carriers without any security measures, which is unfavorable in view of a minimal susceptibility to interference, i.e. a maximal immunity to interference.